For many decades, half duplex two way radio networks have provided reliable and convenient communications using limited shared radio resources. For example, “walkie-talkie” and citizens band (CB) radio networks have enabled users to maintain direct communication channels with other users over extended periods of time. The push-to-talk (PTT) and “instant on” features of half duplex radio devices provide desirable modes of wireless communication for users such as truckers, construction and industrial site personnel, military personnel, taxi dispatchers, police and fire personnel and numerous others. Modern communications systems designed for public safety still typically allocate only one logical media stream in a network, which is shared among network participants. A floor control mechanism then dictates which device in the network is permitted to send media at a given time on a given stream.
Push-to-talk over cellular (PoC) is a recent technology that enables familiar PTT and “instant on” features of conventional half duplex radios, but using mobile communication devices operating over modern cellular telecommunications networks. Using PoC, wireless communication devices such as mobile telephones and notebook computers can therefore function as PTT half-duplex radio devices. Other types of multimedia call models (MMCMs) are also available that provide functionality similar to PoC.
Floor control in a PoC or MMCM session is generally maintained by a PoC or MMCM network server that controls communications between two or more wireless communication devices. When a user of one of the communication devices keys a PTT button, a request for permission to speak in the PoC or MMCM session is transmitted from the user's device to the PoC or MMCM server using, for example, a real-time transport protocol (RTP) message. If no other users are currently speaking in the PoC or MMCM session, an acceptance message is transmitted back to the user's device and the user can then speak into a microphone of the device. Using standard compression/decompression (codec) techniques, the user's voice is digitized and transmitted using discrete voice data packets, such as according to RTP and internet protocols (IP), to the PoC or MMCM server. The PoC or MMCM server then transmits the voice data packets to other users of the PoC or MMCM session, using for example a point to multipoint communication technique.
PoC and conventional PTT radio users sometimes need to monitor more than one wireless communication channel simultaneously. For example, a member of an emergency response network may need to monitor two talk groups, where each talk group is assigned to a specific response team, but where each talk group is broadcasting over a separate logical radio channel. The member of the emergency response network may therefore be required to carry two radios, where one radio is tuned to the first talk group and the second radio is tuned to the second talk group. Alternatively, the member of the emergency response network may repetitively re-tune a single radio, first to one talk group and then to another talk group. However, carrying multiple radio devices or repetitively re-tuning a radio can be inconvenient and inefficient.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.